My big fat SUV

Keeping up with the Jones' is a tough thing to do, and is motivated by, well, the Jones'. This is called 'behavioral contrast' and represents the fact that the goodness of any behavior is not measured by absolute but by relative measures. That is, it hurts when you see other people having bigger cars, fancier houses, and neater lawns than you. So, to alleviate all that hurt, we try to outdo them in the materialism department, and thereby shift to them our pain. Presumably, if our neighbor looks lean and fit, we will take our revenge through a regimen of diet and exercise, and will adduce our new buff physique not to some contagion, but rather a response to our personal pain.

The 'contagion' metaphor is however pretty useful for psychology researchers because it replaces the motivating pain of simple humiliation and envy with some sort of nebulous biological cause that transmits like a dim fog. This makes unremarkable findings seem mysterious and groundbreaking, and certainly grist for more and more studies. This seems to be the case with the recent 'discovery' that hanging out with fat people makes you fat. So your fat is contagious, thus you'd better stay clear of your friends whose girth as well as personalities may be infectious. But this study belies the truth that given the fact that peer pressure is behind all this, being contagious is merely being disingenuous. But hey, that's what happens when you substitute metaphor for reality, a technique psychologists have learned from snake oil salesmen of old.